IDK, sounds (mostly?) like a CYA move. That is, the Counterfeit Apocalypse was coming, but this helps them dodge that. I would think similar for all the bogus reviews and rating. I can hear it now, "Oh. Those? Those aren't __our__ products. We only list them."
I hate to sound like a cynic, but me thinks Amazon's legal team cooked this up, or at least had a heavy hand in it.
I wonder if they'll give all these small sellers the co-mingle option. If they switch to a model where the original vendor pays the extra to not co-mingle, it might indeed address the counterfeit copy. (Buy at MSRP from the original vendor, and be assured that it's genuine, or buy a discount version from another vendor, and take what you get.)
I hate to sound like a cynic, but me thinks Amazon's legal team cooked this up, or at least had a heavy hand in it.